An implantable device designed to articulate the femoral and tibial components of a knee joint prosthesis during primary or revision bicondylar knee joint replacement. It is typically a one-piece contoured polyethylene (PE) insert, or a more complex device (e.g., a guide arm with a stem that is inserted into the tibial tray and a polymer glide) which will better reproduce the flexion of the knee joint due to its capacity for lateral rotation and anterior/posterior movement. This device is typically made of metal and/or a polymer.